The present invention relates to electro-pneumatic brake controllers and, particularly, to an electric motor operated brake controller suitable for establishing pneumatic output pressure for a railroad car brake in a "directs" type electro-pneumatic brake system.
In the evolution of railroad freight train braking from conventional automatic pneumatic control to electro-pneumatic control, as presently envisioned, it is believed that, until all freight cars can be equipped for electro-pneumatic braking, an "indirect" form of electro-pneumatic braking may be initially employed. Such "indirect" brake control implies controlling brake pipe pressure electrically at one or more locations remotely spaced from the locomotive, with the conventional control valve on each car in a train responding to the brake pipe pressure variation in the usual manner to control the car brakes. In this way, faster and more uniform brake response can be achieved throughout a train of railroad cars.
Eventually, however, "indirect" electro-pneumatic control is expected to give way to "direct" electro-pneumatic brake control. Such "direct" electro-pneumatic control implies the electric control of brake cylinder pressure at each car in a train independent of the car control valve device, as opposed to electric control of the train brake pipe pressure to indirectly control brake cylinder pressure.
In direct electro-pneumatic brake control systems, such as shown in U.S. Pat. No. 5,501,512, each car is provided with a microprocessor unit, which receives a control signal corresponding to the level of braking desired. A pressure to electric transducer is employed to provide the microprocessor with a feedback signal consistent with the instantaneous brake cylinder pressure. Solenoid-operated pneumatic valves regulate the brake cylinder pressure according to the difference between these control and feedback signals. Such pressure transducers are known to be sensitive to temperature variations and are expensive to maintain due to the need for periodic calibration, which the afore-mentioned patent addresses. Moreover, the capacity of the solenoid-operated pneumatic valves, as required for brake cylinder pressurization, results in high power consumption for their operation.